The present invention relates to an apparatus and a method for sterilizing container closures.
As generally known, in the food industry and in particular in the field of aseptic filling of containers with beverages and in the field of aseptic food packaging, there exists a need to sterilise the containers both internally and externally before they are filled.
Sterilisation is generally achieved using chemical agents, e.g. hydrogen peroxide, which can be used on surfaces of every type, such as paper, plastic, metal or organic materials.
To ensure that filling takes place in aseptic conditions it is necessary to sterilise not only the containers but also their closures, for example caps or stoppers, which serve to seal the containers at the end of the filling process.
In this light, known apparatuses for sterilizing container closures comprise a conduit having a wall defining internally a passage for the closures.
Hence, said known apparatus defines inside the conduit a closed volume having a controlled aseptic atmosphere. Said known apparatus comprises spraying means for injecting inside the conduit a sterilization fluid (i.e. a chemical agent) heated and vaporized, and drying means for introducing hot air in the conduit. The drying means have the function of eliminating the sterilization fluid condensed on the closures, before the closures themselves exit the apparatus. It is noteworthy to observe that the sterilization fluids which are commonly used in these apparatuses are chemically active when their temperature is above a threshold value (activation value).
For this reason, the sterilization fluid is heated before it is injected in vaporized fashion inside the conduit. In this light, the apparatus comprises a device for heating and vaporising the sterilization fluid, for instance as described in patent application WO2006128884 of the same applicant.
A further problem arises in relation to the need of getting rid of the exhaust fluids which exit from the conduit. In fact, the exhaust fluids exiting from the conduit would flow into the environment surrounding the conduit, if the exhaust fluids were not captured.
In this light, it is noteworthy to observe that the standards fix the threshold values (which must not be exceeded) for the concentration of the exhaust fluids in the environment of the sterilization conduit (in fact, said environment is itself kept aseptic).
Therefore, the sterilization apparatus comprises a system for the extraction of the exhaust fluids, from the conduit, in such a way that they do not flow in the environment.
In the known apparatus, an exhaust tube is provided, which is connected to a suction pump at one end and directly to the conduit at the opposite end. In this way, a suction force is directly applied to the volume inside the conduit.
In this light, a problem arises is relation to the extraction of the exhaust fluids from the conduit.
In fact, said extraction of exhaust fluids generates undesired flows of the process fluids (i.e. the sterilization fluid and the drying air) inside the conduit, thus altering the distribution of the process fluids themselves.
Therefore, the distribution of the process fluids inside the conduit is not optimized because it is affected by the suction force applied by the system for extracting the exhaust fluids.
In addition, the action of the process fluids on the closures is hardly controllable and predictable, due to the fact that the distribution of the process fluids inside the conduit is affected by the extraction of the exhaust fluids.
A further problem arises is relation to the need to activate the sterilization fluid. In fact, because the whole volume inside the conduit must be aseptic, the need arises of securing that the whole amount of fluid present inside the conduit be at a temperature above the activation value.
Thus, it is desirable that also the sterilization fluid that is condensed on the internal surface of the wall of the conduit be active (i.e. above the activation threshold).
For this purpose, in the operation of the sterilization process, the enthalpy of the process fluids (i.e. the sterilization fluid and the drying air) is regulated taking account of the fact that a portion of said enthalpy is needed to heat the conduit wall.
Therefore, in the known apparatus the process fluids (i.e. the sterilization fluid and the drying air), which are oriented towards the closures in order to treat them as described above, heat the fluid filling the volume internal to the conduit 2, and thus indirectly heat the conduit wall 3.
However, this known apparatus has the following drawbacks.
First of all, in the known apparatus the process fluids are not optimized for the treatment (i.e. sterilization) of the closures; in fact, the use of a portion of the enthalpy of the process fluids to obtain the heating of the conduit wall is a waste of energy.
In addition, a use of process fluids which is excessive with regard to the sterilization purposes (excessive with regard to either the flow rate or the temperature of the process fluids themselves) determines a risk of damaging the closures; in fact, en excessive heat is transferred to the closures; in particular, the temperature of the process fluids is too high.
A further prior art is known from document WO 00/21838 disclosing an apparatus for sterilising lids for food packaging.
According to another prior art, document U.S. Pat. No. 5,720,148 discloses a device for filling bottles, especially plastic bottles, with a liquid, wherein said device includes an air separation liquid station, a flash pasteurization station, a station for saturating the liquid with a sterile inert gas with respect to the liquid, a bottle washing station and stoppers with a liquid disinfectant with under hood drying in a treated atmosphere, a bottle filling station, preferably by means of gravity filling under a slight partial vacuum, a station for degassing the inert gas, and a stoppering station.
A further prior art is known from document EP 334216 disclosing methods and means for lid sterilization and temporal sealing.
Document DE 19851654 shows a method and a device for sterilising screwcaps which are treated with atomised hydrogen peroxide, then dried and conveyed to a sanitation chamber for further treatment.